Magnesium sulfate, a byproduct of magnesium hydroxide desulfurization: high-value application in lithium battery electrolyte
I. The intersection of environmental protection and new energy industry
Driven by the "dual carbon" strategy, desulfurization technology in coal-fired power plants, steel coking and other industries is undergoing a revolutionary upgrade. Magnesium hydroxide desulfurization has become a mainstream process due to its high desulfurization efficiency (up to 98.5%) and byproduct resource potential. However, magnesium sulfate produced by traditional processes is often difficult to directly enter the high value-added industrial chain due to problems such as insufficient purity (generally less than 90%) and heavy metal residues. With the explosive growth of the lithium battery industry's demand for raw materials, breakthroughs in the purification and functional modification of magnesium sulfate have transformed it from industrial solid waste into a key new energy material, opening up a new track for the linkage between environmental protection and new energy.
II. Technological breakthroughs in the high-value application of magnesium sulfate
1. Preparation process of pure magnesium sulfate
Magnesium sulfate, a byproduct of traditional desulfurization, is often mixed with magnesium oxide, magnesium sulfite and heavy metal impurities. Through multi-stage gradient crystallization and membrane separation technology, the purity of magnesium sulfate can be increased to more than 99.5%, and the heavy metal content can be reduced to less than 1ppm. The "dynamic countercurrent washing-vacuum evaporation" system developed by an environmental protection technology company in Liaoning has achieved large-scale production of 100,000 tons of battery-grade magnesium sulfate per year, and the product has passed international certifications such as UL and RoHS.
2. Functional development of electrolyte additives
The core value of magnesium sulfate in lithium battery electrolyte:
Enhanced thermal stability: magnesium sulfate molecules can form complexes with lithium hexafluorophosphate (LiPF6), inhibit the decomposition of lithium salts at high temperatures, and increase the thermal runaway temperature of the electrolyte to above 180°C. Experimental data show that the capacity retention rate of the battery increased by 12% after 1,000 cycles of adding 0.5% magnesium sulfate to the electrolyte.
HF capture agent: The magnesium ions in magnesium sulfate react preferentially with free hydrofluoric acid (HF) in the electrolyte to form stable magnesium fluoride precipitation, reducing HF corrosion on positive electrode materials (such as NCM, NCA) and extending battery life. Tests by a power battery company show that after adding magnesium sulfate, the amount of metal dissolution from the positive electrode material is reduced by 65%.
SEI membrane modification: Magnesium ions participate in the formation of a solid electrolyte interface (SEI) membrane rich in MgF₂ on the surface of the negative electrode, which improves the lithium ion transmission rate and inhibits dendrite growth. The silicon-based negative electrode battery using magnesium sulfate modified electrolyte has a volume expansion rate reduced from 280% to 120%, and a cycle life of more than 800 times.
3. Lithium salt precursor conversion
Through ion exchange reaction, magnesium sulfate can be converted into high-purity lithium sulfate, the core raw material of lithium battery electrolyte. The "magnesium-lithium exchange-membrane separation" process developed by a Jiangsu company uses desulfurization byproducts as raw materials. Each ton of magnesium sulfate can produce 0.18 tons of battery-grade lithium sulfate, and the cost is 40% lower than the salt lake lithium extraction route. This technology has been applied to the Qinghai Salt Lake Lithium Extraction Project to achieve the coordinated development of lithium and magnesium resources.
3. Industrial Chain Collaborative Innovation Model
1. Thermal Power-Battery Industry Closed Loop
A power plant in Shandong Province has built an integrated system of "desulfurization-purification-electrolyte":
The magnesium sulfate slurry produced by the desulfurization system is directly connected to the purification workshop through a pipeline, reducing intermediate transportation and storage costs;
The purified magnesium sulfate is directly supplied to surrounding lithium battery electrolyte manufacturers through customized modification;
The magnesium element in the waste electrolyte is recycled and regenerated and re-enters the desulfurization system. This model has increased the power plant's annual revenue by more than 200 million yuan and reduced the electrolyte production cost by 15%.
2. Cross-industry technology grafting
Steel companies deeply process desulfurization byproducts into electrolyte functional materials:
A steel company in Hebei Province jointly developed a "magnesium sulfate-based solid electrolyte" with Chongqing University, using the surplus hydrogen energy of the steel industry to prepare magnesium hydride (MgH₂), and developed a magnesium-sulfur battery with an energy density of 785Wh/kg;
The trace iron in the byproducts is converted into Fe₃O₄ nanoparticles, which are used as negative electrode materials for lithium-ion batteries, realizing the high-value utilization of impurity elements.
IV. Double Leap in Economic and Environmental Benefits
1. Cost Reconstruction
The cost of traditional solid waste treatment is about 300 yuan/ton. After purification into battery-grade magnesium sulfate, the product price can reach 6,000 yuan/ton;
Each ton of magnesium sulfate used as an electrolyte additive can ｒｅｐｌａｃｅ 150kg of lithium hexafluorophosphate, reducing the cost of electrolyte formulation by 18%;
Byproduct resource projects can apply for CCER carbon sink indicators. According to the current carbon price, the annual income of 10,000 tons of production capacity exceeds 5 million yuan.
2. Environmental value-added
The high-value utilization of magnesium sulfate reduces the amount of solid waste generated by the desulfurization system by 90%, avoiding the risk of soil compaction caused by landfill;
HF emissions during the production of electrolytes are reduced by 70%, helping battery companies pass the EU REACH regulation certification.
V. Future technology evolution direction
1. Functional refinement development
Nanoscale magnesium sulfate powder (particle size <100nm) preparation technology improves its dispersibility and interface modification effect in the electrolyte;
The research and development of magnesium-lithium composite electrolyte system takes into account high energy density and safety, and adapts to the iteration of solid-state battery technology.
2. Intelligent production system
The intelligent allocation system based on the industrial Internet matches the desulfurization working conditions and the electrolyte market demand in real time, and dynamically adjusts the magnesium sulfate crystallization process parameters;
The blockchain traceability platform realizes the carbon footprint tracking of the entire life cycle from the desulfurization tower to the battery product, meeting the compliance requirements of the EU Battery Regulation.
3. Global market positioning
The desulfurization transformation of thermal power plants in Southeast Asia and the rise of the new energy vehicle market are happening simultaneously. Chinese technology export companies can provide a packaged "desulfurization-electrolyte" overall solution;
Seizing the right to formulate magnesium-based battery standards, the magnesium-sulfur battery technology developed by Chongqing University has passed the UN 38.3 safety certification, and is preparing to establish an international magnesium battery industry alliance.
The high-value transformation of magnesium hydroxide desulfurization byproducts is reshaping the boundaries between environmental protection and new energy industries. When magnesium sulfate from power plants flows into the electrolyte workshop through pipelines, and when solid waste from steel plants becomes the source of battery innovation, this cross-border chemical reaction is more than just a technological breakthrough, it also heralds a fundamental change in the circular economy paradigm. For companies that are the first to complete the technology layout, every ton of byproduct magnesium sulfate is the key to opening up the trillion-level energy storage market, and is also the pen and ink to write the industry legend in the carbon neutral era.